A representative example of the prior art thermal image printing technique is a printing mechanism shown in FIG. 11 using a thermal head 100 which is adapted to generate heat dotwise according to image signal to transfer an ink on an ink ribbon film 101 to a recording paper 102 so that imagewise printing is effected. Another example is a laser heat mode thermal printing technique shown in FIG. 12 which has been lately studied. In this mechanism, laser beam (LB) which has been emitted by a laser source 110 according to image signal is incident upon a special ink ribbon film 112 through a transparent support 111. The ink ribbon film 112 which has thus absorbed laser beam then generates heat to transfer an ink thereon to a recording paper 113 so that imagewise printing is effected. Shown at 120 in FIGS. 11 and 12 is a platen roll.
Many printing techniques employing such a thermal head have been realized in the form of apparatus. Many full-color printing techniques employing such a thermal head have been reported in Leng Svay et al., "Development of Multi-Head. Full-Color Thermal Transfer Process", preliminary transactions of Japan Hardcopy '89, page 197, Nobuhiro Inoue, "High Resolution Heat Transfer Thermal Printing Head", preliminary transactions of Japan Hardcopy '88, page 250, etc.
A laser heat mode thermal recording technique has already been proposed as disclosed in Mitsuru Irie et al., "Recording Properties of Laser Heat Transfer (3)", preliminary transactions of Japan Hardcopy '91, page 237 and JP-A-4-201485 (The term "JP-A" as used herein means an "unexamined published Japanese patent application").
In the heat-sensitive transfer recording process disclosed in JP-A-4-201485, an infrared-absorbing heat-softening coloring material layer formed on a support is irradiated with laser beam from a semiconductor laser to cause the surface layer of the heat-softening coloring material layer to melt, followed by the contact of the heat-softening coloring material layer with a material to which the coloring material is transferred. In another embodiment of the heat-sensitive transfer recording process, a colorless infrared-absorbing adhesive layer formed on the surface of a heat-softening coloring material layer formed on a support is irradiated with laser beam from a semiconductor laser to cause the surface layer of the adhesive layer to melt, followed by the contact of the adhesive layer with a material to which the adhesive material is transferred.
However, the foregoing conventional techniques have disadvantages. In some detail, the printing technique employing the foregoing conventional thermal head is disadvantageous in that the preparation of a thermal head which provides selective heating in a minute area is technically difficult, making it very difficult on a technical and economical basis to realize a resolution as high as not less than 600 DPI. Thus, the reproduction of a high image quality on an ordinary paper is little feasible at present.
In the laser heat mode thermal recording technique, an infrared-absorbing heat-softening coloring material layer or the like is irradiated with laser beam from a semiconductor laser to cause the surface layer of the heat-softening coloring material layer or the like to melt, followed by the contact of the heat-softening coloring material layer or the like with a material to which the coloring material is transferred, making it possible to provide selective heating in an area almost equal to the diameter of the laser beam from the semiconductor laser and hence realize printing at a resolution as high as not less than 600 DPI despite of thermal recording. However, the laser heat mode thermal recording technique which comprises irradiating an infrared-absorbing heat-softening coloring material layer or the like with laser beam from a semiconductor laser to cause the surface layer of the heat-softening coloring material layer or the like to melt to perform image printing is greatly disadvantageous in that it requires some time until the surface layer of the heat-softening coloring material or the like is melted, inevitably reducing the printing speed and making it difficult to put this printing technique into practical use.